In accordance with a common design in engine lubricating oil pumps, the oil delivered by the pump, i.e. the oil from the high-pressure side of the oil circulation supplied by the pump, is applied to an adjusting member which is used to influence the delivery volume, such as for example a setting ring which can be pivoted. In this way, the delivery volume flow is limited when a particular pressure threshold is reached. Depending on the ancillary constraints of the engine, such as for example the rotational speed of the engine, the temperature of the engine, the need to cool pistons and so forth, an adjustment of the delivery volume—preferably, the specific delivery volume—is often implemented in the form of two or as applicable even more pressure stages, wherein it is alternatively or additionally possible to regulate the pump in accordance with an engine characteristic map, i.e. to perform characteristic-map regulation. In simple cases, pressure can be directly applied to the adjusting member using a manifold valve which is actuated by the engine controller. If the manifold valve cannot be arranged in a housing of the pump or near enough to the pump and/or if, for design reasons, the flow cross-sections in the valve or on the route to or from the valve cannot be dimensioned so as to be sufficient for rapid adjustment, a pilot valve can be provided which controls the application of pressure to or relief of pressure on the adjusting member which can commonly be moved counter to the force of a spring. In such embodiments, a pressure which acts on a partial surface of a pilot piston of the pilot valve, which is typically embodied as a stepped piston, is modulated using the electromagnetically actuated manifold valve.
A pump comprising a pilot valve and additionally an electromagnetic manifold valve is known from each of DE 36 30 792 A1, US 2005/0142006 A1, U.S. Pat. No. 5,876,185 A and WO 2008/037070 A1, which are incorporated by reference. The pilot valve connects the adjusting device, which comprises the adjusting member of the respective pump, with optionally either the high-pressure side of the respective pump circulation or a reservoir for the fluid delivered by the pump or separates the adjusting device from both the high-pressure side and the reservoir. In order to connect the adjusting device to the reservoir via the pilot valve and thus switch to ambient pressure, i.e. an absence of a pressure burden, the pressure fluid is either drained via the pilot valve directly into the environment and flows freely, due to gravity, into the reservoir which is positioned correspondingly low, or has to be guided to the reservoir via a feedback conduit to be provided especially. If it flows off freely, components—for example, components of a vehicle engine—situated in the vicinity of the pilot valve will become contaminated. The fluid flowing off will additionally also become contaminated. On the other hand, the additionally provided feedback conduit leads to an increase in cost. In both cases, aerated fluid is introduced into the reservoir and energy is dissipated needlessly.